Revealing Golgi Architecture: Novel Insights Through Light Microscopy.

The Golgi is a eukaryotic organelle that modifies, sorts, and transports proteins and lipids to their destinations. In mammals, the Golgi is a complex network of interconnected stacks, with each stack made up of closely packed flat membrane sacs called cisternae. The Golgi remains a poorly understood organelle, fraught with controversies despite decades of research. The challenge of visually resolving the cisternal organization of the Golgi under light or electron microscopy contributes to its enigmatic nature. We have developed new imaging methods, including GLIM, en face averaging, and side averaging, to resolve the nocodazole-induced Golgi ministacks. These tools provide new insights into the organization and functions of the Golgi. They enabled us to rapidly and quantitatively investigate cisternal Golgi organization and intra-Golgi transport of secretory cargos. New insights have been revealed about the spatial distribution of Golgi proteins involved in processing and trafficking, the differential partitioning of secretory cargos within cisternae based on their sizes, and the specific Golgi exit sites for constitutive versus signal-dependent secretory cargos. Additionally, the intra-Golgi transport kinetic data acquired from these tools provide a basis for evaluating different intra-Golgi transport models.